Caving is a mining technique in which an ore body or rock mass is undercut under a sufficient area that material caves into the undercut area from which it can be progressively withdrawn, for example, through drawbells into extraction tunnels beneath the undercut. The rate at which caving action progresses is dependent on the rate at which the broken material is extracted.
In ore bodies that are marginally caveable it is possible that instead of continuously caving a stable arch can form if the rock mass is strong enough and it then becomes difficult to promote further caving. U.S. Pat. No. 6,123,394 discloses a method for overcoming problems associated with caving stronger rock by utilising the technique of hydraulic fracturing. By that technique an ore body can be conditioned to promote caving by drilling bore holes into the ore body and initiating fractures at locations within the bore holes by the installation of inflatable packers and pumping hydraulic fluid into spaces between the packers. The ore body may be hydraulically fractured before caving is initiated or after caving has been initiated if necessary to maintain or promote further caving.
Various inflatable straddle tools have been developed for placement within bore holes to initiate hydraulic fracturing. These tools generally have separate spaced packers held apart by rigid steel straddles with hydraulic fluid passages for the supply of hydraulic fracturing fluid to firstly inflate the two separate packers and then to direct fluid to the space between the packers to initiate hydraulic fracturing. Some tools have valving to control and divert the flow of hydraulic fluid between the packers and the space for fracturing. Alternatively, some tools have an external inflation line that is used to inflate the packers separately from the injection fluid. The present invention enables construction of a tool which is of simpler construction and which can be more rapidly deployed and retrieved than conventional straddle packet tools. The invention may also enable initiation of fractures at closer spacing along a bore hole than is possible with conventional straddle packer tools.